Click chemistry for sealants and adhesives

ABSTRACT

The invention described herein generally pertains to a composition that includes a silyl-terminated polymer having silyl groups linked to a polymer backbone via triazole. The silyl-terminated polymer is a reaction product of a functionalized polymer backbone and a functionalized silane. The polymer backbone includes a first functional group, which may be one of an azide or an alkyne. The functionalized silane includes a second functional group may also be one of an azide or an alkyne, but is also different from the first functional group. The functionalized polymer backbone is reacted with the functionalized silane in the presence of a metal catalyst.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 15/975,943, filed May 10, 2018. Application Ser.No. 15/975,943 claims the benefit of and priority to U.S. ProvisionalApplication Ser. No. 62/504,879, filed May 11, 2017. The entireties ofthese aforementioned applications are herein incorporated by reference.

TECHNICAL FIELD

The invention generally relates to polymers useful in coatings,adhesives, and sealants and, in particular, adhesives and sealants madeutilizing click chemistry.

BACKGROUND OF THE INVENTION

Two-part silicone sealants can be produced by an addition cure methodinvolving a platinum catalyst. One method can include, for example, asilicone hydride and a vinyl, which react in the presence of a platinumcatalyst to form an ethyl group bridge between the two components withno additional byproducts. Such platinum catalyzed hydrosilylationsystems, while potentially fast curing, can be easily inhibited by tin,sulfur, or other functionalities present in the system (e.g., amines,etc.).

Further, silyl-modified polymers, such as silyl-modified polyethers (MSpolymers) and silyl-modified polyurethanes (SPUR polymers) are commonlyutilized in adhesives and sealants. In particular, such compositionshave been used in one-component sealants that are moisture cured. Likethe two-part sealants described above, hydrosilylation is often employedto form the silyl-modified polymers used in the moisture-curablesealants.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the present invention, a compositionis provided that includes a silyl-terminated polymer having silyl groupslinked to a polymer backbone via triazole. The silyl-terminated polymeris a reaction product of a functionalized polymer backbone bearing afirst functional group and a functionalized silane bearing a secondfunctional group. The first functional group is one of an azide or analkyne. The second functional group is also selected from the groupconsisting of an azide or an alkyne, but the second functional group isdifferent from the first functional group. The azide-functionalizedpolymer backbone is reacted with the alkyne-functionalized silane in thepresence of a copper I catalyst. The polymer backbone can includepolyether, polyester, polydimethyl siloxane, polymethyl methacrylate,polyacrylate, polybutadiene, or polysulfide.

According to another embodiment, a method is provided for producing acurable composition. The method can include reacting a functionalizedpolymer bearing a first functional group with a functionalized silanebearing a second functional group. The first functional group isselected from a group consisting of an azide and an alkyne. The secondfunctional group is different from the first functional group and can beselected from a group consisting of an azide and an alkyne. The reactionresult is a silyl-terminated polymer having silyl groups linked to thepolymer via a triazole moiety.

In yet another embodiment, a one-part, moisture-curable sealantcomposition is provided. The composition can include silyl-terminatedpolymer having silyl groups linked to a polymer backbone via triazole.The silyl-terminated polymer is a reaction product of a functionalizedpolymer backbone bearing a first functional group comprising one of anazide or an alkyne and a functionalized silane bearing a secondfunctional group, which comprises one of an azide or an alkyne and isdifferent from the first functional group. The composition can alsoinclude a catalyst to promote cross-linking of between silyl groups ofsilyl-terminated polymers.

These and other aspects of this invention will be evident when viewed inlight of the detailed description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention relate to applications of click chemistryin coatings, adhesives, and sealants. Click chemistry involves acycloaddition reaction between alkyne and azide functional groups,typically in the presence of a copper I catalyst, to form a triazolebridge and is pictorially shown below:

The triazole ring is resistant to decomposition via hydrolysis,oxidation, and/or reduction even at high temperature. Moreover, clickchemistry, unlike hydrosilylation, is tolerant to impurities andcompatible with other functionalities in the a system such as amine,sulfur, and tin-based catalysts. Like hydrosilylation, however, clickchemistry provides high yields, relatively simple implementation, anddoes not produce byproducts. Further, while the reaction is exothermic,a the activation energy is sufficiently high enough so that minimaltriazole is formed at room temperature, thus providing working timeand/or pot-life for sealant and adhesive formulations. After activationenergy is reached, the reaction auto-accelerates until completion.Accordingly, click chemistry enable formation of versatile sealant andadhesive compositions incorporating a variety of functional groups.

In accordance with an aspect, click chemistry can be employed to makeone-part moisture curable sealants based on silyl-terminated polymers.The sealant composition includes a polymer backbone, which can bepolyether, polyester, polydimethyl siloxane, polymethyl methacrylate,polyacrylate, polybutadiene, polyurethane, or polysulfide. The sealantfurther includes a catalyst to promote cross-linking of silyl-terminatepolymers in the presence of moisture, such as atmospheric moisture. Thecatalyst may be a tin-based catalyst. In addition, the system mayinclude a moisture scavenger. A hybrid structure, having a combinationof two or more different polymer backbones, can also be contemplateddepending on desired properties of a final structure.

The polymer backbone is modified to include an azide group, which canreact with alkyne-terminated silane to form the silyl-terminatedpolymer. Specifically, the polymer backbone is linked to a silane groupvia a triazole moiety. In an example, the reaction is in the presence ofa copper I catalyst in a solvent such as dimethylformamide, which can beremoved from the system after. This reaction is pictorially illustratedbelow.

The azide group can be introduced in the polymer backbone in a varietyof ways. For instance, a brominated polymer can be functionalized withthe azide group. In particular, the brominated polymer can react with anazide, such as sodium azide in a dimethylformamide solvent as showbelow:

Alternatively, a polymer backbone bearing epoxide groups can befunctionalized with azide groups as shown below:

It is to be appreciated that a transverse arrangement can becontemplated where an alkyne-terminated polymer reacts with anazide-terminated silane. Moreover, as mentioned above, the polymerbackbone can be any polymer such as, but not limited to, polyether,polyester, polydimethyl siloxane, polymethyl methacrylate, polyacrylate,polybutadiene, and polysulfide. In an aspect, the triazole moiety can belinked to the polymer backbone through either an alpha or gamma spacer.

A one-part moisture curable sealant, however, can include hybridsilyl-terminated polymers. For example, two or more different polymerscan bear azide terminal groups and react with alkyne-functionalizedsilane to form silyl-terminated polymers linked via a triazole moiety.

In accordance with another aspect, two-part silicone or epoxy basedsealant and adhesive compositions can be cross-linked via a triazolemoiety formed with click chemistry. The silicone or epoxy components arefunctionalized with azide and alkyne groups and combined using a copperI catalyst. Hybrid two-part systems can also be made with a similarmechanism. For instance, azide-terminated siloxane crosslinks with analkyne-terminated organic polymer. It is to be appreciated that theorganic polymer can bear the azide group and the siloxane bears thealkyne group in such a hybrid two-part system. More generally, hybridpolymers enable combinations of different structural and/or functionalproperties associated with different polymer backbones. Anazide-terminated organic polymer backbone can click with analkyne-terminated inorganic polymer, such as siloxane or polysulfide.The transposition with an alkyne-terminated organic polymer and analkyne-terminated inorganic polymer is also contemplated.

A hybrid polymer can be utilized in connection with other embodimentsdescribed above. For instance, a hybrid polymer can be formed asdescribed above and the hybrid polymer can further be silyl-terminatedvia a further reaction.

In yet another aspect, metal-free adhesive and sealant compositions forelectrical and/or medical applications are contemplated. As mentionedabove, the cycloaddition reaction utilizes a copper I catalyst. Withoutthe catalyst, the reaction typically occurs slowly and yields a mixtureof isomers. With strained alkynes, however, the cycloaddition reactioncan conduct thermally at low temperatures without a metal catalyst.Additional information regarding metal-free or catalyst free clickchemistry can be found in Talena Rambarran et al., Journal of polymerScience, 2015, 53, 1082-1093 and F. Gonzaga et al., Macromolecules,2009, 42, 9220-9224, both of which are herein incorporated by reference.While most adhesives and sealants employ a metal catalyst (e.g.platinum, tin, etc.), metal-free click chemistry with strained alkynesenables formation adhesive and sealant compositions suitable forelectronics applications where presence of a metal catalyst isundesirable.

Metal-free systems can be utilized in combination with other embodimentsdescribed above. That is, strained alkynes capable of reacting with theazide functionality without the metal catalyst can be employed to formthe silyl-terminated polymer, employed in the two-part sealants, oremployed in the formation of the hybrid polymer.

In accordance with another aspect, an on-demand curing sealant isprovided. As mentioned above, minimal triazole forms at roomtemperatures absent a catalyst. By introducing a copper II catalyst, thesame minimal reaction occurs as copper II is inert. Copper II convertsto copper I when exposed to ultraviolet light. Accordingly, a sealantcomposition having a copper II catalyst can be cured, on demand, with UVlight. Alternatively, a reducing agent can be introduced to convert thecopper II to copper I, in situ, to initiate curing. It is to beappreciated that the use of copper II can be combined with thesilyl-terminated, two-part sealants, and two-part hybrid polymerembodiments described above.

According to an aspect, a composition is provided that includes asilyl-terminated polymer having silyl groups linked to a polymerbackbone via triazole. The silyl-terminated polymer is a reactionproduct of: a functionalized polymer backbone bearing a first functionalgroup comprising one of an azide or an alkyne; and a functionalizedsilane bearing a second functional group, which comprises one of anazide or an alkyne and is different from the first functional group.

According to an embodiment of the composition, the polymer backbone isselected from a group consisting of polyether, polyester, polydimethylsiloxane, polymethyl methacrylate, polyacrylate, polybutadiene, andpolysulfide.

According to another embodiment of the composition, the functionalizedpolymer backbone is reacted with the functionalized silane in thepresence of a metal catalyst. In an example, the metal catalyst iscopper I.

According to another embodiment of the composition, copper II is addedto the functionalized polymer backbone and the functionalized silane.The copper II is converted to copper I to effectuate a reaction betweenthe functionalized polymer backbone and the functionalized silane toproduce the silyl-terminated polymer. In one embodiment, the copper IIis converted to copper I via exposure to ultraviolet radiation.According to another embodiment, the copper II is converted to copper Ivia introduction of a reducing agent.

According to yet another embodiment, one of the first or secondfunctional groups is a strained alkyne group capable of reacting anazide group without a metal catalyst.

In a further embodiment, the functionalized polymer backbone is a hybridpolymer comprising an inorganic polymer backbone linked to an organicpolymer backbone. The inorganic polymer backbone and the organic polymerare linked via triazole as a result of a click reaction.

In another embodiment, a method for producing a curable composition isprovided. The method can include reacting a functionalized polymerbearing a first functional group with a functionalized silane bearing asecond functional group. The first functional group is selected from agroup consisting of an azide and an alkyne. The second functional groupis different from the first functional group and selected from a groupconsisting of an azide and an alkyne. The result is a silyl-terminatedpolymer having silyl groups linked to the polymer via a triazole moiety.

According to another embodiment of the method, the reaction is in thepresence of a copper I catalyst.

In another embodiment of the method, the reaction can include addingcopper II to a system including the functionalized polymer and thefunctionalized silane and converting the copper II to copper I toinitiate the reaction. In one example, converting the copper II includesexposing the copper II to ultraviolet radiation. In another example,converting the copper II can include adding a reducing agent.

According to another embodiment of the method, the polymer is selectedfrom a group consisting of polyether, polyester, polydimethyl siloxane,polymethyl methacrylate, polyacrylate, polybutadiene, and polysulfide.

According to another embodiment of the method, a catalyst is included topromote cross-linking of silyl groups in the presence of atmosphericmoisture.

In yet another aspect, a one-part, moisture-curable sealant compositionis provided. The composition includes a silyl-terminated polymer havingsilyl groups linked to a polymer backbone via triazole. Thesilyl-terminated polymer is a reaction product of: a functionalizedpolymer backbone bearing a first functional group comprising one of anazide or an alkyne; and a functionalized silane bearing a secondfunctional group, which comprises one of an azide or an alkyne and isdifferent from the first functional group. The composition also includesa catalyst to promote cross-linking of between silyl groups ofsilyl-terminated polymers.

According to an embodiment of the sealant composition, the polymerbackbone is selected from a group consisting of polyether, polyester,polydimethyl siloxane, polymethyl methacrylate, polyacrylate,polybutadiene, and polysulfide.

The above examples are merely illustrative of several possibleembodiments of various aspects of the present invention, whereinequivalent alterations and/or modifications will occur to others skilledin the art upon reading and understanding this specification and theannexed drawings. In addition although a particular feature of theinvention may have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. Also, to the extent that theterms “including”, “includes”, “having”, “has”, “with”, or variantsthereof are used in the detailed description and/or in the claims, suchterms are intended to be inclusive in a manner similar to the term“comprising.”

This written description uses examples to disclose the invention,including the best mode, and also to enable one of ordinary skill in theart to practice the invention, including making and using anycompositions or products and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that are not different from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal language of theclaims.

The best mode for carrying out the invention has been described forpurposes of illustrating the best mode known to the applicant at thetime. The examples are illustrative only and not meant to limit theinvention, as measured by the scope and merit of the claims. Theinvention has been described with reference to preferred and alternateembodiments. Obviously, modifications and alterations will occur toothers upon the reading and understanding of the specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

What is claimed is:
 1. A method for producing a curable composition,comprising: reacting a functionalized polymer bearing a first functionalgroup with a functionalized silane bearing a second functional group inthe presence of a metal catalyst, wherein the first functional group isselected from a group consisting of an azide and an alkyne; wherein thesecond functional group is different from the first functional group andselected from a group consisting of an azide and an alkyne; and whereinthe result is a silyl-terminated polymer having a first silane group anda second silane group, the first silane group linked to thefunctionalized polymer via a first triazole moiety, and the secondsilane group linked to the functionalized polymer via a second triazolemoiety; wherein the metal catalyst promotes cross-linking of the firstsilane group and the second silane group in the presence of atmosphericmoisture.
 2. The method of claim 1, wherein the metal catalyst is copperI.
 3. The method of claim 1, wherein the reacting further comprises:adding copper II to a system including the functionalized polymer andthe functionalized silane.
 4. The method of claim 3, further comprisingconverting the copper II to copper I to initiate the reaction.
 5. Themethod of claim 4, wherein converting the copper II comprises exposingthe copper II to ultraviolet radiation.
 6. The method of claim 4,wherein converting the copper II comprises adding a reducing agent. 7.The method of claim 1, wherein the polymer is selected from a groupconsisting of polyether, polyester, polydimethyl siloxane, polymethylmethacrylate, polyacrylate, polybutadiene, and polysulfide.
 8. Themethod of claim 1, wherein one of the first or second functional groupsis a strained alkyne group capable of reacting with an azide groupwithout a metal catalyst.
 9. The method of claim 1, wherein thefunctionalized polymer is a hybrid polymer comprising an inorganicpolymer linked to an organic polymer.
 10. The method of claim 9, whereinthe inorganic polymer and the organic polymer are linked via triazole asa result of a click reaction.